The present invention relates to a displacement detection sensor and in particular to a displacement detection sensor using magnetostriction.
One of the conventional displacement detection sensors is disclosed in Japanese Patent Laid-open Print No. Hei7(199 A.D.)-306030 published without examination. In the conventional sensor or device, a wire is connected at one end thereof to a fixed point. The other end of the wire is connected to another fixed point via an in-series provided coil spring. Thus, the wire under such a tension is extended in a direction defined by the two fixed points. The wire also passes through a ring magnet with a clearance which is secured to a body which is movable along the extending direction of the wire.
According to the well-known Wiedemann effect, when a current is applied to the wire placed in a magnetic field of the ring magnet, a twist is produced in the wire. The resultant twist occurs as an elastic wave which travels along the wire. At one side of the wire, the wire is surrounded by a solenoid connected to a microprocessor. When the elastic wave reaches a portion of the wire within the solenoid, a current is induced in the solenoid and such an induction is detected by the microprocessor.
In the foregoing sensor, the elastic wave travels at the speed of sound and therefore, when the current application is established, a first time point is noted. In addition, the induced detection is established at a second time point, and calculating the time duration between the two time points gives ultimately the displacement of the ring magnet.
However, due to the existence of the coil spring at the other end of the wire, the ring magnet fails to move along the fully extended length of the sensor per se. This means that to measure the full scope of the sensor enlargement of the sensor per se in its extension direction is not possible.